A-LevelPhysicsOscillations9702/33 · May/June 2018 · Q220 Marks

In this experiment, you will investigate the motion of an interrupted pendulum.

(a)Set up the apparatus as shown in [Figure 2.1]. • Adjust the string in the split cork so that the distance L between the bottom of the split cork and the centre of the bob is approximately 55 cm. • Measure and record L. L = ........................................................................ • Calculate L/2. L/2 = ........................................................................[1]
(b)(i)• Attach the other boss and clamp and the wooden rod to the stand as shown in [Figure 2.2]. • Adjust the position of the wooden rod so that, when the string is touching the rod, the angle A between the vertical and the string is approximately 14°, as shown in [Figure 2.2]. • Without changing the length of the pendulum, ensure the distance between the wooden rod and the centre of the bob is L/2. • Measure and record angle A. A = ........................................................................[1]
(b)(ii)Estimate the percentage uncertainty in your value of A. percentage uncertainty = ........................................................................[1]
(c)(i)• Pull the bob away from the wooden rod so that the angle between the string and the vertical is 45°, as shown in [Figure 2.3]. • Release the bob. The bob will oscillate and hit the wooden rod. • Determine the period T of these oscillations. T = ........................................................................[2]
(c)(ii)Calculate d where d = sin A / sin 45° d = ........................................................................[1]
(c)(iii)Justify the number of significant figures that you have given for your value of d.[1]
(d)• Move the position of the wooden rod so that angle A is approximately 28°. • Without changing the length of the pendulum, ensure the distance between the wooden rod and the centre of the bob is L/2. • Measure and record angle A and repeat (c)(i) and (c)(ii). A = ........................................................................ T = ........................................................................ d = ........................................................................[3]
(e)(i)It is suggested that the relationship between T and d is T = k (d + 1.707) where k is a constant. Using your data, calculate two values of k. first value of k = ........................................................................ second value of k = ........................................................................[1]
(e)(ii)Explain whether your results support the suggested relationship.[1]
(f)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4.[4]
(f)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. 1. 2. 3. 4.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] (a) Value of L to the nearest mm with unit and in range 50.0–60.0 cm.
[1] (b)(i) Value of A to the nearest degree with unit and in the range 11-17°.
[1] (b)(ii) Percentage uncertainty in A based on absolute uncertainty of 2°-5°. If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to obtain percentage uncertainty.
[1] (c)(i) Value of T in the range 1.20–1.60s with unit.
[1] (c)(i) Evidence of at least two sets of nT where n ≥ 5.
[1] (c)(ii) Correct calculation of d.
[1] (c)(iii) Justification for s.f. in d linked to s.f. in A (or measured angle).
[1] (d) Second value of A.
[1] (d) Second value of T.
[1] (d) Quality: second value of T > first value of T.
[1] (e)(i) Two values of k calculated correctly.
[1] (e)(ii) Valid comment consistent with calculated values of k, testing against a criterion specified by the candidate.
[1] (f)(i) A Two readings are not enough to draw a (valid) conclusion (not "not enough for accurate results”, “few readings”).
[1] (f)(i) B Difficult to measure L with reason e.g. locating centre of bob/parallax/bob or cork gets in the way of the ruler.
[1] (f)(i) C Difficult to measure A or 45° or angle with a reason e.g. no indication of vertical/hard to hold and measure from protractor/hard to hold protractor steady/string too thick/parallax error.
[1] (f)(i) D Problem with bob moving between setting and releasing.
[1] (f)(i) E Difficulty setting rod at L/2 with reason e.g. setting rod and angle at the same time/rod moves when tightening the clamp/rod moves when pendulum hits.
[1] (f)(i) F Difficulty in judging start/end of oscillation.
[1] (f)(ii) A Take many readings (for different values of A) and plot a graph or take more values of k and compare (not "repeat readings" on its own).
[1] (f)(ii) B Improved method of measuring L e.g. measure diameter and add on (or take away) radius from length of string from cork to top (bottom) of bob, or e.g. clear use of pointer(s).
[1] (f)(ii) C Improved method of measuring angle e.g. use a plumb line/clamp protractor/use thinner string, or e.g. shadow projection ideas/photograph and measure angle.
[1] (f)(ii) D Improved mechanism of releasing the bob e.g. clamp bob/use a card gate/add a stop.
[1] (f)(ii) E Mark string.
[1] (f)(ii) F Method of improving timing e.g. put a marker anywhere except at the ends/video with timer (or replay frame by frame).